Automatic variable pitch propeller



lFeb. 28, 1939. RA M. STEPHENS AUTOMATIC VARIABLE FITCH PROPELLER Filed Dec. 20, 1935 S'Sheets-Shet l /NVENTo/a 1Q. M TEP/45N@ BY m J. 7y Ys.

/ Feb. 28, 1939. R M. STEPHENS 2,148,843

AUTOMATIC VARIABLE PITCH PROPELLER Filed Dec 20, 1935 3 Sheets-Sheet 3 oOo oOo all /, f1 NW6.

Patented Feb. 28', 19.39

(UNITED sTATEs PATENT .OFFICE y g aussu- .arsllammgazwm Application December 20', 1935, Serial No. 55,470 '30mm (Cl. 170-132) My invention relates to improvements in automatic variable pitch propellersand an object of the invention is to provide a device oi the character herein described which will change the angular pitch of the propeller blades with a change in air pressure and-thereby change in altitude, the pitch angle becoming greater-as the pressure decreases. 4

A further object of my, invention is to provide a device of the characterherein described which will be entirely automatic in action and requires no attention by the pilot when in ight.

A further' object of my invention is to provide a device of the character herein described which 1I will utilize the full power oi' a supercharged motor at high altitudes. A l A further object of my invention is to provide a device of the character herein described in which the energy for varying the pitch of the propeller 2o blades is derived from air pressure surrounding a hermetically sealed bellows. A further object of my invention is to provide a device of the character herein described which is rugged in construction and will not easily beal; come out oi' order but yet is positive in action and sensitive to relatively slight variations in val1' pressure. A still further object of my invention is to provide a device oi the character herein described which issimple to construct, andA economical to manufacture.

With the above more important'obiects in view and such other'minor objects as may appear as the speciilcation proceeds, my invention consists essentially in the. arrangement and construction of parts all as hereinafter more particularly described, reference being had to the accompanying drawings, in which:

Fig. 1 illustrates a central sectional elevation of my invention, with the racks, pinions and worm gears, however, illustrated in full.

Fig. l2 is a plan view of the invention with the casing partially removed to show the location oi' the actuating mechanism. Fig. 3 is a fragmentary sectional elevation taken on the line l-I Figure 1.

Fig. 4 is an elevational view ofthe bellows and 1 cage used with this invention.

Fig. 5 illustrates a detailed view or the helical v gear and pinions used in the actuating mechanism of my variable pitch propeller.

Fig.l 6 illustrates a sectional elevational view of an alternative method which may be used for rotating the propeller blades on their longitudinal Figure 7 is a further elevational view of my invention similar in general to Figure 1 but showing a conduit leading to Figure 8.

Figure 8 is a sectional elevation oi' the cylinder and hermetically sealed bellows provided within 5 the cockpit of an associated plane.

In the drawings like characters of reference indicate corresponding parts in the diierent figures.

It is commonly known that in internal combustion aeroplane engines in use at the present time, 10 a large percentage of the potentialpower developed by the engine is lost when the plane ascends to high altitudes. This loss of power is due to "the decrease in the weight of air taken in by the carburetor in the rarliied atmosphere. 15

In order to overcome this dimculty, the supercharging of engines has been resorted to with very successful results. VHowever, a supercharged engine equipped with a propeller designed for operation at sea level will not be able to develop full 20 power in the upper thin atmosphere. Increasing the pitch of the propeller will overcome this dii'- ficulty at great altitudes but will reduce the efllciency of the machine in the low atmosphere. Accordingly, variable pitch propellers have been 25 used in order to obtain the correct pitch angle for the air pressure encountered.

These propellers, however, have the disadvantage of necessitating the addition of an extra control in the cockpit of the plane and the pilot has 30 dimculty in adjusting the propeller to obtain the maximum emciency from his engine.

Applicant has accordingly developed a variable pitch propellerl which is entirely automatic in its action and which changes' the pitch of the pro- 35 peller blades with changes in air pressure.

The following description relates to an automatic variable pitch propeller having two blades but it will be evident after a perusal of the descrlptlon that exactly the same principle may- 40 be used in connection with propellers possessing any number of blades.

The i vention consists of a socketed casingl A into cit er side of which are inserted the roots B of the propeller blades. A longitudinally expan- 45' sible bellows C is provided within the casing and gear mechanism D co-acts between the bellows and the blade roots to transmit movement of the bellows to the blades.

The upper part oi' the casing A is in the form 50 `of a short cylinder I having opposed longitudilaterally into the gear housing and immediately l subjacent 'thereto` are the opposed sockets 4 for casing, extends between the sockets andcloses the lower end of an upstanding cylinder II which is in alignment with the aforementioned cylinder I. Integral annular iianges I2 are provided on the louter face of theA cylinder Il, the longitudinal axes of which are coincident with those of the roots 5 of the propeller blades within which they extend. Beneath the plate I0, a further short cylinder I3 extends downwardly and is furnished at its extremity with an encircling hub flange I4 provided with a plurality of apertures l5 therein for attachment to the companion crank shaft i ange of the aeroplane engine.

The casing, itshould be noted, is constructed in two identical halves which are fastened together by passing bolts through orifices I5' within lugs I 6 situated on either side of the longitudinal recesses 2 and also through lugs I1` and Il' on opposing sides of the encircling socket flanges 1. Further orifices are drilled within the casing between the cylinder I3 and the plate I 0 and bolts are passed therethrough to aid in firmly holding the two halves of the casing in integral relationship. The upper end of the cylinder I is externally threaded and provided with a, cap I8 having an encircling internally threaded flange I9, the threads of which engage with those upon the cylinder I.

Within the reamed portion 9 in the root sockets is placed a ball thrust bearing 20 consisting of rings 2| having opposed ball races 22 cutin the faces thereof and interposed between these rings is placed .the ball cage 23 carrying the ball bearings 24 ltherein which engage within the ball races 22. v

In order to prevent this bearing 20 from slipping oii` the roots of the blade, an internally threaded collar 25 is screwed upon the root against the bearing and a further collar 26 having an inwardly converging face 21-is tightened against the collar 25 and constitutes a lock nut to hold that collar firmly in place.

An encircling channel 28 is cut within the col` lar 26 facing the central axis of the propeller, this channel being provided for the purpose of catching'and retaining oil which otherwise would be thrown out past the bearings and along the blade of the propeller by the centrifugal force of the rapidly rotating device. When the propeller Stops, the oil which has been retained within the channel is immediately released and serves t0 aid lubrication of the device when the engine is restarted.

Further bearings 29 are furnished to facilitate the rotative movement of the propeller blades on their longitudinal axis. Annuli 30, carrying on their outer peripheries the inner ball race, are firmly/*attached over the flanges I2. The customaryfball cage 3|, carrying the ball bearings 32, is inserted between the annuli 30 and further annuli 33 which are inserted in the ends of the roots of the propeller blades by reaming out a. portion of the said blades and pressing the annuli home to engagement with ShOllldClS 3.4 Produced by tha reaming.

It should here be mentioned that the upstanding cylinder I I acts as a stop to prevent the blades from moving towards the central axis of the device and thus disengaging the thrust bearing 20 when the propeller is in a stationary condition.

Within the aligned cylinders 2 and II', I provide a cylindrical metallic bellows 35 composed of brass orother suitable material. This bellows is securely attached to the plate I0 by means of a plurality of bolts 36 fastened to the lower edges thereof, the heads ofthe bolts being countersunk in circular recesses 31. 'I'hese bolts, it should be noted, are tightened sufficiently to'hermetically seal the bellows and prevent any entrance of air thereinto or discharge therefrom.

'Ihe upper end of the bellows is closed and sealed by a substantial metallic disc 38 and over the bellows and attached to the disc 38 is placed a light yet strong cylindrical cage 39. Longitudlnally extending apertures 40 are cut around the sides of the cage and between these apertures are provided ridges 4I. When the cage'is within the cylinders II and I, these ridges just bear against the sides thereof and so reduce the friction between the cage and the cylinders. The upper' end of the cageis closed by a disc 42 which is attached as before mentioned to the companion disc, upon the upper end of the bellows 35.

Diametrically opposed on either side of the cage 39, are attached rack plates 43 by means of rivets 44 passing through orices therein and also through aligned orifices within the cage. Upon each rack plate integral therewith are provided a pair of spaced parallel longitudinally extending racks 45. The racks 45 are designed to engage with pinions 46 attached to either side of a short cylinder 41 through which is passed a shaft 48 journalled within bearings 49 within either side of the gear casing 50. On the outer sides of the pinions 46 are fastened by means of bolts 5I, ball race plates 52 provided with ball races 53 therein to engage with rball bearings 54 carried within bearing cages. The ball bearings 54 are designed to rotate within a further ball race 56 machined within the inner opposed faces 51 of the gear casing 50.

It will be noted that around thecylinder 41 is placed a single helical rib 58. This rib does not extend completely'around the cylinder and the side walls of the rib are twisted Withrespect to the longitudinal surface of the cylinder in order that the rib may mesh correctly at all times between bearings immediately to be described.

'I'hreadably attached Within orices 59 in the roots 5 of the propeller blades are a pair of adjacent pins 60 provided with lock nuts 6I to prevent them from becoming accidentally disengaged from the orifices 59. Stub shafts 62 project through the lock nuts 6I and upon these shafts are placed ball bearings 63 having the usual inner and outer annul 64 and 65 respectively carrying opposed ball races and the ball bearings inserted therebetween. The outer sur*- faces of the annuli' 65 are designed to engage against either side of the helical rib 58 so that rotative movement of the pinions 46 will cause a slight angular displacement of the roots of the propeller blades.

It has already been mentioned that the side walls of the helical rib 58 are obliquely disposed with respect to-the surface of the cylinder 41, the reason for this being that as the cylinder rotates in a clockwise or anti-clockwise direction from the point where the central portion of the rib thereby decreasing the ultimate length of the lbearings are moved together with the root of the blade to right or to left so that when either yorder that the bearing faces of .the bearings .63

may always lie parallel and against the side walls of the rib 58 at each point upon the length thereof, the rib must be machined to an increasing obliquity towards each end.

If so desired, instead of using the pins B provided with the bearings thereon and thesingle helical rib 58, I may'make use ofthe embodiment shown in Figure 6 of the drawings accompanying this application which consists of metallic rings 66 circumscrlbing the inner end-of the blade roots and being attached thereto by a plurality I of countersunk screws 61 passing through the rings 66 into the blade root.

Upon the upper surface of this ring are cut a number of teeth 68 to engage with a worm gear 69 substituted in place .of the cylinder 41 and tooth 58 described in the first embodiment.

It will be noted that within the bellows' 35, extends an upwardly disposed sealedv dome l0. This dome is by no means an essential part of the apparatus and may be 'dispensed with if necessary and its function will be shortly described. I

The structure of my improved type of automatic variable pitch propeller having now been described, its mode of operation will be herewith end ofthe cage. resting upon the upper suro face of the plate I 0. In this position, the pro- Apeller blades possess their minimum angular ,pitch. However, if the device is now'moved to a vhigher. altitude where the.. air becomes raried,

the pressure on the upper surface of the bellows will decrease and consequently the air therein will expand and tend to open the bellows. This will 'cause an upward movement of the cage 39 and a consequent turning of the pinions 46 by the' racks 45. 'I'he rotation of the helical tooth 58 engaging between the bearings 63 will cause a longitudinal turning effect of the propeller blades to take place and the device is so adjusted .that this turning effect will increase the angle of pitch of the blades.

- Consequently, the greater the altitude. of the engine to which this device is attached, the greater willbe'the expansion of the bellows and theA greater the pitch angle of the propeller blades,

would cause an abnormal expansion thereof,

thereby requiring an excessively long cylinder. To keep the length of the cylinder within desired limits, the above mentioned dome 10 may be -placed within the'bellows to displace a certain within the bellows.

amount of. air-which is thus unable to expand For. this reason, it cannot bellows under reduced external pressure.

.In cases where it may be necessary to increase the amountof energy delivered by the bellows 35, I would, of course, increase the diameter of the bellows, thereby increasing the cross sectional area thereof and obtaining a greateramount of pressure therefrom. However, increasing the. 'size of the bellows might require that the hub of the propeller be made abnormally large and in order to overcome this diiiculty, I use an auxiliary bellows in the following manner.

, Within the cockpit of the plane or in any other convenient location, is -placed a rigid metal cylinder 1| closed at either end, which is provided withan hermetically sealed bellows 12 therein similar to the bellows 35 within the hub of the propeller but having a larger diameter to deliver -a greater amount of energy. Within'this bellows, I may also place a dome 'I3 similar to the dome -10 within the propeller.

'I'he space 14 between the outside of the auxiliary bellows and the rigid casing is filled with oil or futher non-compressible uid and a tube l5 leads from this oil chamber to the inside of the bellows 35 within the propeller hub which isl likewise nlled with-oil. It will now be apparent that .if the pressure around the bellows 35 should decrease, a correspondingdecrease in pressure would occur within the bellows 35 which would be transmitted through the oil tube l5 to the oil chamber 'i4 around the auxiliary bellows.

that it' possesses a greaterdiameter than the bellows within the hub of the plane, this expansion would deliver more power to the bellows within 'I'hus the bellows 'i2 would expand and it will be noted` the hub than if this bellows wasaufuled and jected.

Since various modifications can be made in the above invention, and many apparently widely different embodiments of sane, made -within the scope of the claims without departing vfrom the spirit and scope thereof, it is intended that all matter contained in the 'accompanying specification shall be interpreted as illustrative only and not in`a limiting sense and I desire only such limitations placed thereon as are specically expressed in the accompanying claims.

What I claim as my invention is:` 1. Improvements in variable pitch propellers comprising a casing, `a cylinder within said casing, bellows within said cylinder, a cage upon said bellows, twin racks upon the sides of said cage,

pinions meshing with said racks, a cylinder.

sockets provided in said casing, bearings mounted.

upon said blades, said helical rib passing between said bearings andmeans for attaching said propellerto an aero engine.

2.` Improvements in variable pitch propellers comprising a casing, a cylindrical portion within said casing provided with longitudinal recesses extending down the sides thereof, outwardly opening sockets upon thesides of said cylindrical portion and a hub ange attached to said casing,

an expansible and contractible cylindrical bellows roots or said blades, secondary bearings mounted within said cylindrical portion, acage upon said upon said blades, said xibs passing between said bellows, twin racks upon the sides of said cage, bearings to transmit rotative movement o f said twin pinions engaging with said' racks, cylinders ribs to said blades. V

interposedbetween each pair of said twin pinions, 3. 'I'he device as claimed in c1aim'2 in which 6 helical ribs extending around said cylinders, roan air displacing dome is positioned within saidV tatable propeller blades extending within said bellows.

sockets and mounted upon thrust and radial l ROBERT M. STEPHENS.

bearings, an oil retaining collar encompassing the 

